EXHIBIT 5.1

                                   November 2, 2001

Plug Power Inc.
968 Albany-Shaker Road
Latham, New York 12110

Ladies and Gentlemen:

     Re:  Registration Statement on Form S-8
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     This opinion is delivered in our capacity as counsel to Plug Power Inc.
(the "Company") in connection with the preparation and filing with the
Securities and Exchange Commission under the Securities Act of 1933, as amended
(the "Act") of a Registration Statement on Form S-8 (the "Registration
Statement") relating to additional shares of Common Stock, par value $.01 per
share (the "Registered Shares") which the Company may issue pursuant to the 1999
Stock Option and Incentive Plan, as amended, (the "Plan").

     As counsel for the Company, we have examined a copy of the Plan and the
Company's Amended and Restated Certificate of Incorporation and the Amended and
Restated By-laws, each as presently in effect, and such records, certificates
and other documents of the Company as we have deemed necessary or appropriate
for the purposes of this opinion.

     We are attorneys admitted to practice in The Commonwealth of Massachusetts.
We express no opinion concerning the laws of any jurisdiction other than the
laws of the United States of America, The Commonwealth of Massachusetts and the
Delaware General Corporation Law.

     Based on the foregoing, we are of the opinion that upon the issuance and
delivery of the Registered Shares against payment therefor in accordance with
the terms of the Plan and any agreement thereunder, the Registered Shares will
be legally issued, fully paid and non-assessable shares of the Company's Common
Stock under the General Corporation Law of the State of Delaware.

     The foregoing assumes all requisite steps will be taken to comply with the
requirements of the Act, applicable requirements of state laws regulating the
offer and sale of securities and applicable requirements  of The Nasdaq Stock
Market, Inc.

     We hereby consent to being named as counsel to the Company in the
Registration Statement and to the inclusion of this opinion as an exhibit to the
Registration Statement.

                              Very truly yours,

                              /S/ GOODWIN PROCTER LLP

                              GOODWIN PROCTER LLP